Sarah Keegan
Headquarters, Washington, D.C.
March 14, 1991
(Phone: 202/453-2754)
Linda S. Ellis
Lewis Research Center, Cleveland, Ohio
(Phone: 216/433-2900)
RELEASE: 91-40
ARCJETS YIELD BETTER PERFORMANCE, LONGER SATELLITE LIFE
NASA's Lewis Research Center, Cleveland, has the lead role in
developing the arcjet thruster technology recently selected for
stationkeeping use on AT&T's Telstar 4 communications satellites.
Arcjet systems offer a significant improvement in propellant
use over chemical and other electrically-augmented thrusters. The
savings realized can be used to increase a satellite's on-orbit
lifetime or payload mass. Alternatively, launch mass can be
decreased so that a smaller rocket booster can be used.
The arcjet research and technology program at Lewis Research
Center began in 1983. A major objective was to bring advanced
electric propulsion to operational status. This included
component research necessary to demonstrate the required
performance, life and integration issues associated with the
arcjet system.
In an arcjet, a direct current electrical arc is used to heat
the decomposition products of hydrazine propellant to very high
temperatures. Although the arc core temperature can reach 31,123
degrees F, the nozzle walls are protected by a cool gas boundary
layer.
The hot, slightly ionized gas exits the rocket nozzle at an
average velocity 1.5 to 2 times that attained in conventional
thrusters. For example, the 1.8 kW arcjet systems developed by
Rocket Research Co. (RRC), Redmond, Wash., for the Telstar 4
program, provide a specific impulse (thrust divided by the
propellant consumption rate) of about 500 seconds.
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This compares to a state-of-the-art resistojet system
(another type of electrical thruster) that would provide 300
seconds of specific impulse for the same task. The 1.8 kW design
is modeled closely after a flight-type 1.4 kW system developed by
RRC under a Lewis-sponsored program.
Switching to arcjet systems for north-south stationkeeping on
a geosynchronous communications satellite can reduce propellant
requirements by several hundred pounds. This savings can extend
satellite lifetime by more than 50 percent or allow the satellite
to shift to a less powerful, less expensive launch vehicle.
The arcjet technology developed by NASA's Lewis Research
Center and U. S. industry is the most advanced in the world. The
Telstar 4 thrusters are the only arcjets accepted for operational
use on a spacecraft.
Lewis and industry continue to study arcjet thruster systems
and their interactions with host spacecraft systems. Results to
date suggest that electromagnetic interference with satellite
systems should be minimal and that there will be no problem
sending radio signals through the thruster exhaust plume.
Lewis researchers also are investigating a range of power
options to enhance the versatility of hydrazine arcjet
technology. Examples include low power (1 kW) systems for
power-limited satellites and high specific impulse systems for
advanced communications satellites. The use of high specific
impulse hydrogen arcjet systems also is being explored for
primary propulsion.
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NOTE TO EDITORS: A photograph is available to illustrate this
release by calling the Audio Visual Branch at 202/453-8375. The
order number for color photographs is 90-HC-255; for black
and white prints, 90-H-220.